UK Tax Codes: What 1257L, BR, D0 and K Codes Mean

Your tax code is the short string of numbers and letters on every payslip that tells your employer how much tax to deduct. Millions of people are on the wrong code at any given time, quietly overpaying or underpaying every month. Learning to read yours takes two minutes and is one of the highest-value checks in UK personal finance.

How to read a tax code

The number is your tax-free allowance divided by ten: 1257 in the standard code 1257L means £12,570 of income before any tax. The letters describe your situation:

Why codes go wrong

The most common triggers are changing jobs (especially without a P45), taking a second job, receiving taxable benefits like private medical insurance or a company car, and HMRC carrying forward an out-of-date estimate of your income. Job changes are the classic case: start a new role mid-year without paperwork and you will often land on an emergency code, taxed with no cumulative adjustment until HMRC catches up.

What a wrong code costs

On a £30,000 salary, being switched from 1257L to BR means losing the benefit of your entire Personal Allowance through payroll, an overpayment of roughly £210 a month until corrected. The reverse error, underpaying through a too-generous code, is worse: HMRC will reclaim it later, usually by squeezing next year's code. If your payslip deductions look wrong, compare them against our salary calculator, which assumes the standard code, and investigate any gap.

How to check and fix your code

1. Find your code on your latest payslip, P60, or in your HMRC personal tax account.
2. Check the number reflects your real allowance: £12,570 standard, adjusted for benefits, Marriage Allowance, or the taper above £100,000 (see the income tax guide).
3. Update your employment details, benefits and estimated income in the personal tax account. HMRC recalculates and sends the new code to your employer automatically.
4. Overpaid tax from earlier in the current year normally comes back through your next payslip once the corrected cumulative code is applied. For previous years, HMRC issues a P800 calculation or you can claim a refund directly on GOV.UK.

When your code should not be 1257L

A non-standard code is often correct. Marriage Allowance moves 10% of allowance between partners (codes M and N). Taxable benefits reduce the number. Earnings above £100,000 taper the allowance away entirely, and high earners with company benefits commonly hold K codes. The test is not whether your code looks unusual, but whether the allowance it encodes matches your actual circumstances.